Mr Shearer says National broke with convention by failing to even discuss the nomination with Labour.

"We haven't had any conversations with the Government, so clearly they've just made that [decision] unilaterally," Mr Shearer told NZ Newswire.

"At the end of the day, the speaker is the referee, if you like, in Parliament; the umpire in Parliament, and it's always good to have somebody there who we all respect and who we all have at least some say in."